Like AW, my first thought is a poor connection. I would also check the connectors and crimping. My second guess is that the yellow wire was made of better copper. Just a better wire. My third thought is if your phase is off somewhere, or maybe you have a week fet or something that is putting more stress on the two phases that got hot.

I usually solder all the wires I can because of the potential of connector failure. If I go with connectors the one's I feel best about are bullet connectors. For phase wires, 5mm at least. 6mm are probably better. Easy to solder, and then shrink rap to keep them from coming apart.

These kind:

Bullet Con.jpg (33.13 KiB) Viewed 426 times

Favorite Quote: "This is L.A., sugar. There is no 'over the top." --- Chris Erskine

If you examine the damage closely, you will see that the heating is not in the wire proper (no melted insulation) and not in the bolted connection (no discoloration in the bolt or plastic insulator block), it's in the crimp. The discoloration in the ring terminal starts at the terminal crimp where things are melted and fades away towards the bolt.

For some reason that we can't see because the heat shrink didn't melt, the yellow wire had an effective crimp whereas the other two did not. Looking at the visible crimps in the two melted wire runs, there is really no useful crimp - the sleeve is just folded into place over the wire and really is pretty ineffective.

The crimp should be broad and completely crush the ring terminal sleeve with the wires inside into a solid block of copper with a gas-tight seal. You need a much better crimper (ratcheting, etc). Use the more expensive thicker copper terminals as well - not the cheap thin junk.

crimpNG.jpg (249.53 KiB) Viewed 421 times

There is nothing wrong with bolted connections - they were the standard in the automotive industry for the better part of a century and are still used where high currents are present. They are essentially impervious to vibration and make an excellent electrical connection as long as the underlying bolt has a shoulder against which the ring terminal is tightened or the housing is bakelite (hi-temp and doesn't flow under pressure to allow things to loosen). The only reason they are not prevalent in ebikes is because of the size and inconvenience. If you can afford the space, keep on using them, but get your connectors attached to the wire properly.

Last edited by teklektik on Feb 13, 2018 5:21 pm, edited 1 time in total.

Just about anything is better that those yellow terminal blocks. I've seen so many of those melt down. Bullet connectors, Anderson Power Poles (not the generic copies) or just straight crimping them together all will be better than the yellow block.

Yes, it could be that those yellow blocks go hand in hand with the terrible poorly plated tiny ring terminals. But if you assume the crimps were all about the same quality (not a great assumption) then seems like how tight the nut is staying could have a lot to do with uneven heating. Modern gold plated plugs are pretty water proof these days too. Hard to keep humidity out of the blocks in wet weather. During heavy heating and cooling cycles maybe springy connectors are better?

Sometimes solder can wick up the wire strands and make a hard spot that after the wire is flexed a lot breaks the strands, and uncleaned flux can hide down in the wire... properly done crimps have proven to be a hard to beat method, but like most things, dependent on the right tools and technique.

I've read that crimps can withstand a level of heat that would re-melt a soldered connection. However, my personal opinion is that no joint should ever get so hot that any solder that is present would be damaged.

I'm not sure on the specifics but...it's also bad to get copper extra hot (hardening? Brittleness? Oxidation?).

I'd bump up the size of wire for as much length as you can easily reach, and use brand new connectors that are also one size larger. Wire and connectors are cheap, and my time is valuable to me...I don't like breakdowns.

Solder melts at about 370°F (188°C) If your connectors are that hot, you have a problem. And yes, solder can harden a bit of the wire, but lo less then the crimp. Wires often fray at the end of a crimp thereby lessening the conductive capability of wire. I have seen that more often then with soldered wires, or soldered bullet connectors.

Favorite Quote: "This is L.A., sugar. There is no 'over the top." --- Chris Erskine

Everybody has their own favorite techniques of course. Some of it is application specific too... I make a lot of boat wiring harnesses, and the boat wiring codes are anti solder for some connectors. Then there's other ones like assembling the sevcon multi pin connectors where you can't really solder them and still have the pins fit in the plugs reliably. But they have the special terminals and crimpers, with tabs that grab the insulation on the wire for stain relief.
I think I got my anti solder bias from all the customer batteries I've seen killed by a simple broken off soldered balance wire or BMS wire.

If you examine the damage closely, you will see that the heating is not in the wire proper (no melted insulation) and not in the bolted connection (no discoloration in the bolt or plastic insulator block), it's in the crimp. The discoloration in the ring terminal starts at the terminal crimp where things are melted and fades away towards the bolt.

You're right, but I can't see that in the tiny thumbnail (even if I enlarge it locally) that shows up in the OP's post. If the link in it is supposed to go to a larger image, it doesn't for me (just a blank page with various script errors).

If the image had been attached to the post directly where I could view the full size version, I might've been able to see that.

So, to the OP, I'm sorry about the misdirection of where the problem lies.

I like to bet both problems existed. a bad crimp caused the nut to heat, loosening it.

Go with the big fat bullet connectors IMO. Because you likely are not an expert crimper. If you were, I'd suggest something like a 45 amps Anderson, but with 6 sets of connectors. Each crimp then carrying half the load.

I don't know why people relay on crimps anyway. It is such a spotty connection style. Solder it! Even if it is crimped I solder it to make sure.

Solder conducts like crap in your joints making hot spots that if stressed melt and flow places they can short out on things.
Solder in the wire strands means broken wires if you bend them a few times.
Soldered joints can not match the electrical impedance of a proper cold-forged crimp joint, nor the mechanical strength (because the solder itself is low tensile strength, and when wicked into strands creates stress riser failure points.)

Solder is a mega-fail for performance EVs, but is better than most of the garbage insulated crimp connectors and crimpers you can buy at a hardware store. Any useful crimp joint will be non-insulated, and require a real crimper to cold-forge.

Each carcinogen vapor exposure includes a dice roll for cancer.

Each mutagen vapor exposure includes a dice roll for reproductive genetic defects in your children.

Each engine start sprays them into a shared atmosphere which includes beings not offered an opportunity to consent accepting these cancer experiences and defective genetics life experiences.

Every post is a free gift to the collective of minds composing the living bleeding edge of LEV development on our spaceship.

I don't know why people relay on crimps anyway. It is such a spotty connection style. Solder it! Even if it is crimped I solder it to make sure.

Solder conducts like crap in your joints making hot spots that if stressed melt and flow places they can short out on things.
Solder in the wire strands means broken wires if you bend them a few times.
Soldered joints can not match the electrical impedance of a proper cold-forged crimp joint, nor the mechanical strength (because the solder itself is low tensile strength, and when wicked into strands creates stress riser failure points.)

Solder is a mega-fail for performance EVs, but is better than most of the garbage insulated crimp connectors and crimpers you can buy at a hardware store. Any useful crimp joint will be non-insulated, and require a real crimper to cold-forge.

Glad I read this thread, I'm going to cease adding solder to my crimp joints and invest in a better crimper. Been using one of my grandpa's old crimpers (decent, he was a master electrician back in the day) but I'm going to get myself a ratcheting crimper and redo all my connections with quality bullet connectors.